1. Field of the Invention
The present invention relates to the field of antennas, more particular to an antenna system which is capable of sharing a common antenna to achieve functions of amplitude modulation and frequency modulation.
2. The Related Art
With rapid development of mobile communications, the mobile phone, as a portable electrical device, has incorporated many functions for meeting user's requirements. For example, some mobile phones have the functions of amplitude modulation and frequency modulation for receiving broadcast program by an antenna system of the mobile phone. Conventionally, the antenna system of the mobile phone has two individual antennas. The individual antennas are adapted for matching with a frequency modulation (FM) matching circuit for achieving the FM function and an amplitude modulation (AM) matching circuit for achieving the AM function, respectively. That is, a user can operate the mobile phone to achieve both AM and FM functions through the separate antennas.
However, because mobile phones have been developed toward the miniaturization and the multifunction, such antenna system is not optimal. Adversely, the mobile phone needs to remain a biggish space for mounting the separate antennas, which will add the volume of the mobile phone or have an influence on the reasonable assembly of other electrical components of the mobile phone. In addition, it is particularly cumbersome to mount the separate antennas in the mobile phone. So it is required to design an antenna system used for a mobile phone which is capable of achieving the functions of AM and FM via a common antenna.